Plasma waves between Saturn and its moon Enceladus

Artitst's concept of Enceladus and Saturn (Image NASA/JPL-Caltech)
Artitst’s concept of Enceladus and Saturn (Image NASA/JPL-Caltech)

Two articles published in the journal “Geophysical Research Letters” describe studies concerning the planet Saturn’s system based on information obtained from the Cassini space probe during what was called the Grand Finale, the orbits close to Saturn performed in the weeks preceding the end of that extraordinary mission. In particular, the audio was generated that contains sound obtained by converting the electromagnetic emissions discovered between Saturn and its rings and Enceladus generated by movements of plasma between them.

The mission of the Cassini space probe ended on September 15, 2017 but the analysis of data collected during years of work continues, in particular those collected in the weeks that preceded its destruction in Saturn’s atmosphere. During those final orbits, Cassini carried out a series of maneuvers that in previous years would have been considered too risky because it traveled into areas where it was impossible to assess the danger that there might be something that could damage the space probe. During these weeks, very interesting data were collected.

On September 2, 2017, during one of the last orbits, Cassini’s Radio Plasma Wave Science (RPWS) instrument detected electromagnetic waves traveling on the magnetic field lines that connect Saturn and Enceladus, one of its most interesting moons thanks to the presence of a ocean of liquid water under its icy crust. Those lines have been compared to an electrical circuit between the two celestial bodies with energy flowing back and forth.

Radio waves that transmit radio broadcasts are also electromagnetic emissions that get converted into the sounds we hear. Similarly, Dr. Ali Sulaiman of the University of Iowa, one of the members of the RPWS team, together with his colleagues made a similar conversion starting from the electromagnetic waves generated by the plasma that moves between Saturn and Enceladus.

The result is not exactly a symphony but a whooshing that allows us to perceive plasma waves by ear. Ali Sulaiman explained that Enceladus is a small generator around Saturn and is immersed in the planet’s magnetic field. The plumes of water vapor emitted by the moon are now well known thanks to Cassini: they’re ionized and fill the environment around Saturn. The new discovery is that there’s an electromagnetic response from the planet in the form of plasma waves along the lines of its magnetic field that interact with Enceladus.

The Earth and the Moon don’t interact that way while similar interactions between Saturn and its rings were already known. As it normally happens in space probe missions, even after the end of its mission, Cassini allowed to discover something new about the complex and extraordinary Saturn system.

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